Explanation:
The sum of the given numbers is:
15 + 17 + x + 28 + 39 = 99 + x
To find the missing value, we can use the formula for the mean (average):
mean = (sum of numbers) / (number of numbers)
Substituting the given values:
23 = (15 + 17 + x + 28 + 39) / 5
Multiplying both sides by 5:
115 = 15 + 17 + x + 28 + 39
Simplifying:
x + 99 = 115
x = 16
Therefore, the missing value is 16.